This invention relates to data communications systems, and more particularly to methods of translating service names to network addresses of service providers in a local area transport protocol used in a communications network.
In U.S. Pat. No. 4,823,122, issued Apr. 28, 1989, assigned to Digital Equipment Corporation, assignee of this invention, a local area network is disclosed which is capable of interconnecting terminals with service providers using a communications link. The terminals are coupled to the link by interface units called servers which handle network protocol functions for the terminals. One of the functions provided by the servers is that of translating service names to network addresses. The terminals send requests to the servers for network services using the name (function) of the service rather than the address of the service provider. To perform the translation operation, the server may accumulate service advertisements periodically sent by the service providers, generating a service directory. When the server then receives a request from one of its terminals, the service directory is searched to find the service name and its corresponding network address of the provider of this service. Storage of the service directory places a burden on the server in large networks in that a large amount of memory must be provided. To reduce the memory requirements at the server, the service providers can be assigned group codes, and the server can then store only the service advertisements for its assigned group codes. The maintenance of the group codes imposes an additional burden, however, since user intervention is required to select the groups of providers, and to select the group codes to be copied by each of the users. The group codes must be carefully configured to avoid using excess memory space in the servers, but yet make sure each type of user has information available for each service it may ever need to use. To reconfigure the system when changes are made, the manager of the service providers (usually systems manager), and the network manager, must agree on group codes, then each one must set up the changes on the system and the servers. That is, due to the requirement for establishing and setting up group codes, a new user terminal cannot be merely plugged into the system and used immediately because the terminal must be assigned group codes consistent with its server or else the server must be reconfigured.